FEATURES OF GEOMETER’S SKETCHPAD

http://www.youtube.com/watch?v=LKnf3dVz2rw

 

(transfer from fiona303.wordpress.com dated 14th September 2010 to nurfiona-chung.blogspot.com)

We have to learn how to draw points, circles, line segments, rays, and lines.

The Measure menu will explored, including how to measure angles, lengths, perimeter, and also use the Geometer Sketchpad’s built-in calculator.

Then we will also learn how to choose options from the Construct menu for objects such as parallel lines, perpendicular lines, midpoints, angle bisectors, etc.

Point : Locate and left-click on the point button which is located on the left side of our screen. The arrow that is controlled by our mouse should now have a red dot at the tip of it. Left-click anywhere in the drawing window and a point will appear. Draw several points in the window.

Circle : Locate and left-click on the circle button which is located on the left side of our screen. To draw a circle, left-click in the window. A point marking the center of the circle will appear. Now drag our mouse until the circle has the desired radius. Then left-click again.

Line : Locate and left-click on the line button which is located on the left side of our screen. If we click quickly, the default is to draw line segments. However, if we hold the left mouse button down while on the line button, a menu appears that allows us to choose between line segments, rays, and lines. Explore each of these options and draw a few line segments, rays, and lines in our window.

Select : Locate and left-click on the select button which is located on the left side of our screen (it is the arrow that points up and left). Left-click on some of the objects that we have already drawn (e.g. points, lines, and circles).

The purpose of the select action is clear when we use the Measure and Construct menus.

Measure menu : Locate the drop-down measure menu at the top of our window. We will notice numerous options. However, we may not be able to choose most of these. This depends upon which objects are, or are not, currently selected. Options such as Angle, Area, and Distance require that certain objects are selected before these options can be chosen.

For example, to measure distance we can select two points. To measure an angle, select three points that define the angle. Experiment with some of the other options in the Measure menu and see which kinds of objects must be selected to use the option in question – What is the difference between distance and length?

Caution : Often we may find that an option under the Measure menu is unavailable to us even though we selected the required objects. Usually this means that some extra things are selected that should not be. This is particularly problematic in complicated diagrams with a large number of objects. The best thing to do if this occurs is to left-click in an open area of our window. This un-selects everything. Then we can re-select only those objects that we need.

Construct menu : Locate the drop-down construct menu at the top of our window. We will notice numerous options. As before, we may not be able to choose most of these, depending upon what is, or is not, currently selected.

For example, draw a line segment in our window and make sure it is the only object selected.

What options are available to us from the Construct menu?

Try them and see what happens.

i) To construct parallel and/or perpendicular lines, draw a line (ray or segment will also work) and a point not on the line (see picture below). Make sure both are selected. Go to the Construct menu and choose Parallel Line or Perpendicular Line.

ii) Next draw two line segments that meet at a common vertex to form an angle. Make sure both line segments are selected. Go to the Construct menu and look for Angle Bisector. Notice that this option is not available to us. It appears that Geometer’s Sketchpad expects a different collection of objects to use this option. Figure out which objects need to be selected and then bisect your angle using the Angle Bisector. Go back to the Measure menu and measure our original angle. Then measure the two smaller angles to verify that our angle was indeed bisected. This activity could easily be done using a protractor and a compass. However, now let us see the advantage of dynamic geometry software. Left-click on one of the vertices from our original angle and start dragging it around the screen. In the upper left corner of our window we should see the angle measure changing as we move the vertex. In addition, the measure of the two smaller angles are also changing.

iii) Now draw a circle and plot two distinct points on the circle. Select both points and the circle. Choose Arc On Circle from the Construct menu. Notice that there are actually two different arcs that connect our points on the circle.

iv) Draw a circle in our window. With the circle selected choose Circle Interior from the Construct menu. Select and de-select the interior and notice the effect. With the interior selected measure the area inside the circle. Also, measure the radius and circumference of the circle. Change the radius of our circle by dragging the point on the circle (not the center) around the screen. Notice that the area and circumference are also changing as we do this.

v) Explore the other options under the construct menu.